In core drilling, a core tube is suspended inside a drill string for receiving a core sample of ground being cut by a core drill. The core tube is coupled to the head assembly enabling the core tube to be: lowered into the drill string and locked in place while a core sample is being cut and, subsequently retrieved from the drill string once the drilling is ceased to enable the core sample to be analyzed. The head assembly comprises a spear point at an up hole end which engages an overshot attached to a wire line. To lower the head assembly and core tube through the drill string the overshot is engaged with the spear point and the wire line is wound out so that the head assembly travels by action of gravity down the drill string. To prevent the core tube being pushed back by an advancing core sample being cut by the core drill, the head assembly may also comprise a latching system which engages a latching seat, such as a recess or shoulder inside the drill string. When the head assembly is to be retrieved an upward force applied by the wire line is transmitted via the head assembly to the latching system to disengage from the recess or shoulder enabling the head assembly to be retrieved from the core drill.